1. Field of the Invention
The present invention relates to coating compositions for textile floor coverings.
2. Discussion of the Background
Heavy coating compositions for carpets based on amorphous poly(alpha-olefins) (APAO) have been known for years in addition to those made of asphalt, PVC, and polyurethane mixtures. A typical formulation is made up of approximately 30% of a thermoplastic binder and 70% of a filler. Examples of binders are atactic polypropylene (APP) of various grades (product of homo- or copolymerization) or specific atactic co- and terpolymers. From the last mentioned group, propylene/1-butene/ethylene terpolymers, propylene/ethylene, 1-butene/ethylene, and 1-butene/propylene copolymers have proved particularly useful.
Isotactic polypropylene (IPP), resin, wax, or paraffin can optionally be added for selective modification of properties. Powdered limestone is used primarily as filler, and also barite in some cases.
The solid coating composition is ordinarily applied as a hot-melt adhesive to the underside of carpet materials treated in various ways, that carry a latex or hot-melt precoat. In this regard, for example, refer to B. H. Korner, "The Use of Atactic Polypropylene Using The Example of Solid Carpet Coating", Kunststoffe 65, pages 467 f., 1975, incorporated by reference herein. Carpet tiles are the preferred field of use for the coating compositions.
With increasing use of carpet tiles in residences, hospitals, banks, etc., the specifications for a good solid coating composition are constantly increased. The deficient stability under Load of the carpet tiles made with atactic polyolefins is frequently criticized. Under high Load, such as under legs of chairs or tables, or when walked on with high heels, permanent impressions are made or damage occurs that impair the lay or the dimensional stability of the tiles. The reasons for this is the plastic deformation of the coating composition under the influence of a load. This phenomenon is called "cold flow".
Cold flow can be reduced by adding IPP or by using higher molecular weight atactic polyolefins. However, the flexibility, and thus the lay, are unfavorably affected by this. Problems can also occur in processing because of the increased melt viscosity of the composition. In addition, solid coating compositions with high proportions of IPP tend to shrink because of the recrystallization process. To achieve a balanced property profile, it is therefore generally attempted in practice to limit the addition of IPP to the amount that is just necessary.
There is therefore a strongly felt need for a solid coating composition that can be processed by the conventional hot-melt technique and also has the property of partial elastic recovery in addition to a low depth of penetration under load, i.e., low cold flow.